The proliferation of a vast variety of wireless applications, such as cellular communications, WLAN, GPS, has created co-existence issues. This is especially prevalent in modern, miniaturized cellular handset transceivers, as such devices can have multiple, concurrently operating transmitters and receivers working over a wide frequency range.
There are several mechanisms that can result in spurious response in a receiver. A particularly troublesome one is caused by the harmonic response of switching mixers commonly used in transmitter and receiver chains. In a receiver chain, for example, a switching mixer down-converts an input frequency signal to generate an output signal at a lower frequency, fIF. However, while the switching mixer down-converts the desired signal at fLO, the local oscillator frequency, it also down-converts harmonic frequencies, to fIF, causing contamination of the desired signal.
In view of the foregoing, it would be desirable to provide a circuit that filters harmonic responses for a switching mixer. In particular, it would be desirable to produce a low-power, low noise, stable circuit that rejects harmonics responses in a switching mixer.